In the past, avionics engineers have attempted to extend the life of fluorescent lamps used to backlight liquid crystal displays in aircraft. The complete failure of a lamp could be catastrophic and at the least it requires much effort in bulb replacement. Consequently, it is desirable to extend the life of fluorescent lamps for avionics displays.
One attempt that has been utilized in the past is a dual filament approach where if one filament fails another remains. Typically, these filaments have a common terminal and are arranged in a "V" shape in one plane. Another frequent application has been to utilize two parallel filaments in the same plane. While these designs have enjoyed considerable acceptance in the industry, they have several serious drawbacks. First of all, the "V" shape suffers from the occasional tendency of a broken filament to damage the unbroken filament. Secondly, both the "V" shaped design and the parallel filament design suffer from a reduction in filament life due to the transport of material from the filament to the glass wall (evaporation/deposition). This "pumping" reduces filament life by accelerating the loss rate of emissive material. Emissive material loss rate is minimized if the filament-wall distance is maximized, that is, if the filament is centrally positioned along a diameter of the glass tube. Since current dual filament designs do not possess this attribute, there exists a need for improvement in fluorescent lamps for avionics displays.
Consequently there exists a need for improvement in fluorescent lamps for avionics displays.